Systems and methods for image quality enhancement for multi-head camera

ABSTRACT

A system is provided that includes a gantry, detector units, and at least one processor. The gantry defines a bore. The plural detector units are mounted to the gantry and configured to rotate as a group with the gantry in rotational steps. Each detector unit is configured to acquire imaging information while sweeping about a corresponding axis. The at least one processor is configured to determine a region of interest (ROI) of an object; identify a set of detector units; for the identified set of detector units, determine a sweeping configuration that results in a predetermined percentage of projection pixels receiving information from the ROI; determine a rotational movement configuration for the gantry using the determined sweeping configuration; and control the gantry and the set of detector units to utilize the determined rotational movement and sweeping configurations during acquisition of imaging information.

BACKGROUND

The subject matter disclosed herein relates generally to medical imagingsystems, and more particularly to radiation detection systems.

In nuclear medicine (NM) imaging, such as single photon emissioncomputed tomography (SPECT) or positron emission tomography (PET)imaging, radiopharmaceuticals are administered internally to a patient.Detectors (e.g., gamma cameras), typically installed on a gantry,capture the radiation emitted by the radiopharmaceuticals and thisinformation is used, by a computer, to form images. The NM imagesprimarily show physiological function of, for example, the patient or aportion of the patient being imaged.

An NM imaging system may be configured as a multi-head imaging systemhaving several individual detectors distributed about the gantry. Eachdetector may pivot or sweep to provide a range over which the detectormay acquire information that is larger than a stationary field of viewof the detector. Focus-based acquisition may improve image quality in afocused region. Obtaining good image quality of all features in afocused region requires sufficient time for acquisition of allprojections observing the region, and failure to acquire sufficientlywide coverage of a region of interest may result in distortions due tonoise, for example if edge projections are not included in a focusedregion. However, on the other hand, increasing the width of coverage mayresult in an overall increase in scan time.

BRIEF DESCRIPTION

In accordance with an embodiment, a nuclear medicine (NM) multi-headimaging system is provided that includes a gantry, plural detectorunits, and at least one processor. The gantry defines a bore configuredto accept an object to be imaged, and is configured to rotate about thebore. The plural detector units are mounted to the gantry and configuredto rotate as a group with the gantry around the bore in rotationalsteps. Each detector unit is configured to sweep about a correspondingaxis and acquire imaging information while sweeping about thecorresponding axis. The at least one processor is operably coupled to atleast one of the detector units, and is configured to determine a regionof interest (ROI) of the object to be imaged; identify a set of detectorunits from the plural detector units mounted to the gantry; for theidentified set of detector units, determine a sweeping configurationthat results in a predetermined percentage of projection pixelsreceiving information from the ROI; determine a rotational movementconfiguration for the gantry using the determined sweepingconfiguration; and control the gantry and the set of detector units toutilize the determined rotational movement and sweeping configurationsduring acquisition of imaging information. It may be noted, for example,that in various embodiments, the order of various steps may be revised.For example, the rotational configuration may be determined before thesweeping configuration, or the determinations may be performedalternately in an iterative fashion.

In accordance with another embodiment, a nuclear medicine (NM)multi-head imaging system is provided that includes a gantry, pluraldetector units, and at least one processor. The gantry defines a boreconfigured to accept an object to be imaged, and is configured to rotateabout the bore. The plural detector units are mounted to the gantry andconfigured to rotate as a group with the gantry around the bore inrotational steps, with each detector unit configured to sweep about acorresponding axis and acquire imaging information while sweeping aboutthe corresponding axis. The at least one processor operably coupled toat least one of the detector units, and is configured to determine aregion of interest (ROI) of the object to be imaged; for at least one ofa number of different total rotational step combinations, determine gapsresulting between detector views for each rotational step combination;determine a number of rotational steps to be used based on the gaps; andcontrol the gantry and the set of detector units using the determinednumber of rotational steps during acquisition of imaging information.

In accordance with another embodiment, a method is provided foracquiring imaging information with a nuclear medicine (NM) multi-headimaging system. The system includes a gantry and plural detector units.The gantry defines a bore configured to accept an object to be imaged,and is configured to rotate about the bore. The plural detector unitsare mounted to the gantry and configured to rotate as a group with thegantry around the bore. Each detector unit is configured to sweep abouta corresponding axis and acquire imaging information while sweepingabout the corresponding axis. The method includes determining a regionof interest (ROI) of the object to be imaged. The method also includesidentifying a set of detector units from the plural detector unitsmounted to the gantry. Further, the method includes, for the identifiedset of detector units, determining a sweeping configuration that resultsin a predetermined percentage of projection pixels receiving informationfrom the ROI. Also, the method includes determining rotational movementconfiguration for the gantry using the determined sweepingconfiguration. The method further includes controlling the gantry andthe set of detector units to utilize the determined rotational movementand sweeping configurations during acquisition of imaging information.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides a flowchart of a method, according to an embodiment.

FIG. 2 illustrates an example gantry having 8 detector units configuredto move with the gantry in rotational steps according to an embodiment.

FIG. 3 provides a flowchart of a method, according to an embodiment.

FIG. 4 illustrates example rotational steps and corresponding gapsbetween views, according to an embodiment.

FIG. 5 depicts an example group of detector views that are at the sameview angle, according to an embodiment.

FIG. 6 depicts an example group of detector views.

FIG. 7 illustrates an example sweep range boundary, according to anembodiment.

FIG. 8 illustrates an example detector system, according to anembodiment.

FIG. 9 provides a schematic view of an example detector system,according to an embodiment.

FIG. 10 provides a schematic view of a nuclear medicine (NM) imagingsystem according to an embodiment.

FIG. 11 illustrates a detector arrangement according to an embodiment.

DETAILED DESCRIPTION

The foregoing summary, as well as the following detailed description ofcertain embodiments and claims, will be better understood when read inconjunction with the appended drawings. To the extent that the figuresillustrate diagrams of the functional blocks of various embodiments, thefunctional blocks are not necessarily indicative of the division betweenhardware circuitry. Thus, for example, one or more of the functionalblocks (e.g., processors, controllers or memories) may be implemented ina single piece of hardware (e.g., a general purpose signal processor orrandom access memory, hard disk, or the like) or multiple pieces ofhardware. Similarly, the programs may be stand alone programs, may beincorporated as subroutines in an operating system, may be functions inan installed software package, and the like. It should be understoodthat the various embodiments are not limited to the arrangements andinstrumentality shown in the drawings.

As used herein, the terms “system,” “unit,” or “module” may include ahardware and/or software system that operates to perform one or morefunctions. For example, a module, unit, or system may include a computerprocessor, controller, or other logic-based device that performsoperations based on instructions stored on a tangible and non-transitorycomputer readable storage medium, such as a computer memory.Alternatively, a module, unit, or system may include a hard-wired devicethat performs operations based on hard-wired logic of the device.Various modules or units shown in the attached figures may represent thehardware that operates based on software or hardwired instructions, thesoftware that directs hardware to perform the operations, or acombination thereof.

“Systems,” “units,” or “modules” may include or represent hardware andassociated instructions (e.g., software stored on a tangible andnon-transitory computer readable storage medium, such as a computer harddrive, ROM, RAM, or the like) that perform one or more operationsdescribed herein. The hardware may include electronic circuits thatinclude and/or are connected to one or more logic-based devices, such asmicroprocessors, processors, controllers, or the like. These devices maybe off-the-shelf devices that are appropriately programmed or instructedto perform operations described herein from the instructions describedabove. Additionally or alternatively, one or more of these devices maybe hard-wired with logic circuits to perform these operations.

As used herein, an element or step recited in the singular and precededwith the word “a” or “an” should be understood as not excluding pluralof said elements or steps, unless such exclusion is explicitly stated.Furthermore, references to “one embodiment” are not intended to beinterpreted as excluding the existence of additional embodiments thatalso incorporate the recited features. Moreover, unless explicitlystated to the contrary, embodiments “comprising” or “having” an elementor a plurality of elements having a particular property may includeadditional such elements not having that property.

Various embodiments provide systems and methods for improving imagequality. Various embodiments balance an increased width in coverage of aregion of interest (ROI) with gantry rotational positions or steps toallow use of relatively wide coverage while reducing or optimizing arelatively low number of focus views. Accordingly, scan time may bereduced while maintaining image quality. Various embodiments provideimproved scan efficiency using a flexible scan design, in which primarydetectors cover the ROI using more time for focused acquisition of theROI, while remaining detectors are utilized to provide more scanningtime on background acquisition. Further, various embodiments provide forefficient planning of scans including selection of a number ofrotational steps or positions of a gantry, and/or shifts or offsets forrotational steps or positions of a gantry.

A technical effect of at least one embodiment includes improved imagequality. A technical effect of at least one embodiment includes reducedacquisition time and/or reduced injected dose. A technical effect of atleast one embodiment includes improved providing of adequate coverage ofa ROI. A technical effect of at least one embodiment includes improvedpositioning of detectors along rotational steps taken by a gantry.

FIG. 1 provides a flowchart of a method 100 for controlling detectorheads of a multi-head imaging system and/or reconstructing an imageusing focused and non-focused (or background) imaging information(including edge and interior information) acquired with detector headsof a multi-head imaging system in accordance with various embodiments.The method 100 (or aspects thereof), for example, may employ or beperformed by structures or aspects of various embodiments (e.g., systemsand/or methods and/or process flows) discussed herein. In variousembodiments, certain steps may be omitted or added, certain steps may becombined, certain steps may be performed concurrently, certain steps maybe split into multiple steps, certain steps may be performed in adifferent order, or certain steps or series of steps may be re-performedin an iterative fashion. It may be noted, for example, that in variousembodiments, the order of various steps may be revised. For example, therotational configuration may be determined before the sweepingconfiguration, or the determinations may be performed alternately in aniterative fashion. In various embodiments, portions, aspects, and/orvariations of the method 100 may be able to be used as one or morealgorithms to direct hardware (e.g., one or more aspects of a processingunit discussed herein) to perform one or more operations describedherein.

At 102, an object to be imaged is positioned in the bore of a NM imagingsystem (e.g., system 1000 discussed herein). In various embodiments, theNM imaging system includes a gantry and plural detector units attachedto the gantry. The gantry defines a bore in which the object to beimaged (e.g., human patient) is disposed. The gantry rotates about thebore, with the plural detector units mounted to the gantry andconfigured to rotate as a group with the gantry around the bore inrotational steps. Also, each detector unit is configured to sweep abouta corresponding axis and acquire imaging information while sweepingabout the corresponding axis.

At 104, a region of interest (ROI) of the object to be imaged isdetermined. Generally, the ROI corresponds to or includes a portion ofthe object that is of particular diagnostic interest. For example, theROI may be determined to include an organ (or organs) that are to beevaluated by a scan, and may include a buffer region around the organ(or organs) to insure complete inclusion of the organ (or organs) in theROI. In some embodiments, the ROI may be specified by a user (e.g., viainputting a boundary of the ROI via a touchscreen or other inputdevice). In some embodiments, the ROI may be located automatically byone or more processing units from an attenuation map and/or anatomicallandmarks, for example.

At 106, a total number of rotational steps to be taken by the gantry isdetermined. FIG. 2 illustrates an example gantry 200 having 8 detectorunits 210 disposed about a bore 220. In a first rotational step 230,shown in solid lines, the detectors 210 are at a first position. In asecond rotational step 232, the detectors 210 are in a second position,shifted ten degrees clockwise from the first position. Additionalrotational steps may be employed in various embodiments, for example, upto the point at which a given detector is positioned where its adjacentdetector was originally positioned.

Various techniques may be employed to determine the total number ofrotational steps in various embodiments. For example, FIG. 3 provides aflowchart of a method 300 for determining the number of rotationalsteps. It may be noted that the method 300 (or aspects thereof), forexample, may employ or be performed by structures or aspects of variousembodiments (e.g., systems and/or methods and/or process flows)discussed herein. In various embodiments, certain steps may be omittedor added, certain steps may be combined, certain steps may be performedconcurrently, certain steps may be split into multiple steps, certainsteps may be performed in a different order, or certain steps or seriesof steps may be re-performed in an iterative fashion. In variousembodiments, portions, aspects, and/or variations of the method 300 maybe able to be used as one or more algorithms to direct hardware (e.g.,one or more aspects of a processing unit discussed herein) to performone or more operations described herein.

At 302, gaps (gaps that result between detector views) are determinedfor at least one of a number of different total rotational stepcombinations. For each rotational step of the gantry, the detectorsmounted to the gantry may have gaps therebetween for each view angle.For example, FIG. 4 illustrates example rotational steps andcorresponding gaps between views. As seen in FIG. 4, at the firstrotational step 410 (e.g., an uppermost detector located at a 12:00position), for any given viewing angle, gaps may appear between theviews provided by adjacent detectors. For example, at about a 46 degreeviewing angle, view 415 depicts the gaps 416 between adjacent detectorsfor the first rotational step 410.

As seen in FIG. 4, second rotational step combination 420 includes thedetector positions provided by the first rotational step 410 along witha second rotational step 422, with each detector moved one increment inthe clockwise direction from the first rotational step 410 to the secondrotational step 422. View 425 depicts the gaps 426 between the detectorviews at the 46 degree viewing angle for both the first and secondrotational steps combined. As seen in FIG. 4, the gaps for therotational step combination 420 are smaller than those for the firstrotational step 410 alone.

Similarly, third rotational step combination 430 includes the detectorpositions provided by the first rotational step 410 and secondrotational step 422 along with a third rotational step 432, with eachdetector moved one increment in the clockwise direction from the secondrotational step 422 to the third rotational step 432. View 435 depictsthe gaps 436 between the detector views at the 46 degree viewing anglefor the first, second, and third rotational steps combined. Also, fourthrotational step combination 440 includes the detector positions providedby the first rotational step 410, second rotational step 422, thirdrotational step 432, along with a fourth rotational step 442, with eachdetector moved one increment in the clockwise direction from the thirdrotational step 432 to the fourth rotational step 442. View 445 depictsthe gaps between the detector views at the 46 degree viewing angle forthe first, second, third, and fourth rotational steps combined (in theillustrated example, there are no gaps in view 445). Likewise, fifthrotational step combination 450 includes the detector positions providedby the first rotational step 410, second rotational step 422, thirdrotational step 432, and fourth rotational step 442, along with a fifthrotational step 450 with each detector moved one increment in theclockwise direction from the fourth rotational step 442 to the fifthrotational step 452. View 445 depicts the gaps between the detectorviews at the 46 degree viewing angle for the first, second, third,fourth, and fifth rotational steps combined.

As seen in FIG. 4, as more rotational steps are added to thecombination, the gaps become smaller until the fourth rotational stepcombination 440, at which point the gaps are eliminated. Accordingly,any additional rotational steps are unnecessary and would result inunnecessary additional scanning time.

Returning to FIG. 3, at 304, a number of rotational steps to be used isdetermined based on the gaps. For example, the number of rotationalsteps may be selected to ensure a minimum average gap size, or asanother example, to ensure a minimum size of the largest gap. In someembodiments, the number of rotational steps is determined to satisfy apredetermined maximum threshold gap size (e.g., the size of the largestgap present). For example, with reference to FIG. 4, if thepredetermined threshold gap size is zero, in the illustrated example,the fourth rotational step combination 440 would provide the desiredzero gap and fourth rotational steps would be selected. In otherembodiments, the maximum threshold gap size may be larger than zero andthe third rotational step combination 430, for example, may provideacceptable results.

It may be noted that in various embodiments, the gap may be determinediteratively. For example, gaps resulting for an initial number ofrotational steps may be determined and compared to a threshold. If thethreshold is satisfied, the initial number of rotational steps may beused as the number of rotational steps used to control the gantry anddetectors during imaging. However, if the threshold is not satisfiedusing the initial number of rotational steps, the number of rotationalsteps may be increased. For example, the number of rotational steps maybe iteratively increased by one until the resulting steps satisfy thethreshold.

Additionally or alternatively, in various embodiments, a scan of the ROImay be acquired (e.g., a preliminary scan that includes enoughinformation to determine a general outline or boundary of the ROI),and/or a boundary of the ROI may be provided via a user input. Next asize of the ROI may be determined. It may be noted that the size of theROI may include values in 2 or 3 dimensions taken at various portions ofthe ROI, so that the size also indicates the shape of the ROI. Thenumber of rotational steps may be determined based on the size of theROI. For example, a predetermined relationship between ROI size andnumber of rotational steps may be utilized. In some embodiments, alookup table may be used. For example, the ROI may be approximated as anellipse having a defined long axis and a defined short axis. The ellipserepresenting the ROI may then be compared to a listing of ellipses withknown corresponding numbers of appropriate rotational steps, and thenumber of rotational steps for the listed ellipse that most closelymatches the ellipse representing the ROI may be used. As anotherexample, the smallest listed ellipse that completely bounds the ROI maybe identified, with the number of rotational steps for the smallestbounding listed ellipse used as the number of rotational steps. It maybe noted that, in some embodiments, the number of rotational stepsdetermined based on the size of the ROI may be used as the initialestimate of rotational steps of an iterative process as discussed above.It may be noted that, in various embodiments, the use of look-up tablesand predetermined ellipse sizes need not necessarily be limited to usewith ROI's and/or focused scans. For example, the use of look-up tablesand predetermined ellipse sizes may be used for an entire body and/orfor unfocused scans.

Various sub steps may be employed to determine the number of rotationalsteps. For example, in the example embodiment depicted in FIG. 3, at306, detector positions and angles are determined for all view providedby the detectors for the rotational step combination. Each view providedby each detector at each rotational step may be determined. At 308, thedetector views are arranged in bins according to view angle. Forexample, FIG. 5 depicts an example group 500 of detector views that areat the same view angle 510 that would be binned together at 308.

At 310, each detector view of each bin is projected along the view angleto find a start and end position for each corresponding detector. Forexample, FIG. 6 depicts an example group 600 of detector views. As seenin FIG. 6, example detector 602 has a start position 610 and an endposition 612. At 312, the maximum gap between projected views isdetermined. For example, the gap may be determined by the distancebetween the start and end positions of adjacent projected views from310. As seen in the example of FIG. 6, the maximum gap is the gap 620between the end position 612 of detector 610 and the start position 614of adjacent detector 616. At 314 of the illustrated example, the largestgap of the maximum gaps (e.g., the group of individual maximum gaps fromeach bin) is determined, and used in determining the number ofrotational steps.

With the number of rotational steps determined, at 316, the gantry anddetector units are controlled using the determined number of rotationalsteps during acquisition of imaging information.

Returning to FIG. 1, at 108, a set of detector units is identified fromthe plural detector units mounted to the gantry. In some embodiments,the set of detector units is all available detector units, while inother embodiments the set of detector units is a subset of all availabledetector units. For example, the set of detector units selected may be aset of detector units best suited for imaging the ROI, while otherremaining detector units not selected are better suited for imagingbackground aspects of the object being imaged, and/or may be utilized toacquire information of a more narrow field of view including the ROIthan the selected set of detector units. In the illustrated embodiment,at 110, the detectors of the subset are identified based on at least oneof a proximity to the ROI or corresponding attenuation to the detectorunits. For example, those detectors disposed closest to the ROI may beused to more efficiently provide information on the ROI. Similarly,those detectors having less attenuation between the detector and the ROImay be used to more efficiently provide information on the ROI.

At 112, for the identified set of detector units, a sweepingconfiguration is determined. In various embodiments, the sweepingconfiguration is determined to result in a predetermined percentage ofavailable pixels (e.g., a percentage of projection pixels as discussedin connection with FIG. 7 below) receiving information from the ROI. Thesweeping configuration in various embodiments specifies where eachdetector sweeps (e.g., defines a sweeping boundary for each detector ofthe subset) at a given rotational step of the gantry (or at eachrotational step of the gantry when multiple gantry rotational steps areutilized). The sweeping boundary, for example, may specify two viewangles bounding the sweep range. The sweeping configuration in variousembodiments may also specify a sweeping speed. It may be noted that thepredetermined percentage of pixels may vary among detector units withinthe identified set and/or outside of the identified set.

FIG. 7 illustrates and example sweep range boundary (e.g., boundary of arange of view angles over which a given detector sweeps duringacquisition of imaging information). As seen in FIG. 7, a detector unit700 is used to image an ROI 702 of an object 704 (e.g., human patient).As depicted in FIG. 7, the detector unit 700 is at an edge of a sweepboundary along a sweeping direction 710, with a corresponding field ofview 720 that includes part of the ROI 702 and part of a backgroundportion 703 of the object 704. As seen in projection 730 of pixels 732,a percentage of pixel columns 734 collect information regarding the ROI702. The sweeping configuration at 112 in various embodiments is set sothat the percentage of pixel columns collecting information at the sweepboundary or edge of sweeping zone is a predetermined percentage (e.g.,50% of pixel columns receive information of the ROI at the sweepboundary). For wider coverage (e.g., to insure adequate coverage of theROI by selected detectors) a relatively low percentage may be utilized,while a higher percentage may be utilized to provide more narrowcoverage.

FIG. 8 illustrates an example detector system 800 having a first set ofdetector units 810 (e.g., detector units identified at 108) and a secondset of detector units 820 (e.g., detector units not identified at 108)being used to image an object 802 having an ROI 840. The first set ofdetector units 810 have a relatively wide range of coverage 812. Such awide range of coverage helps insure adequate coverage of the ROI forimproved image quality over the entire ROI. In various embodiments sucha wide range of coverage may be selected only for a set of detectors(e.g., set 810) depending on proximity to the ROI 804 and/or attenuationconsiderations. For the remaining detectors (second set of detectorunits 820), a narrower range 822 may be employed, thereby, for example,adding flexibility to scan design and required scanning time.

Returning to FIG. 1, at 114, a rotational movement configuration isdetermined for the gantry, using the determined sweeping configuration.The rotational movement configuration in various embodiments specifieshow and when the gantry rotates during imaging acquisition. For example,the rotational movement configuration in various embodiments includesthe number of gantry rotational steps (e.g., as determined at 106 orotherwise). The rotational movement configuration may also specify thesize of the steps, and/or an offset or shift for the steps. Therotational movement configuration may be determined, for example, toprovide a minimal number of views from the identified detector set foreach rotational step, while providing adequate coverage of the ROI. Asanother example, the rotational movement configuration may be determinedto provide a minimal number of views from the identified set ofdetectors summed over all rotational steps, while providing adequatecoverage of the ROI. In various embodiments, the number of viewsrequired to provide a desired ROI coverage may be calculated orotherwise determined for a number of rotational movement configurations,with the configuration providing the best number selected.

It may be noted that utilizing a wide coverage as discussed herein maytend to lead toward a relatively larger number of focused long-timeprojections during the sweeping of some detectors. Further, dividing aset scan time between a larger number of focused projections may resultin lower time-per-projection and a related loss of photon counts, lowersignal to noise ratio (SNR), and/or reduced image quality. In variousembodiments, the gantry position may be shifted to beneficially providethe number of views required to achieve the required ROI coverage. Forexample, an optimal or improved gantry position may be calculated ordetermined for a given ROI to provide a reduced or minimal number ofviews (e.g., for each step or for all steps combined, or a weightedcombination of views for each step and total views for all stepscombined). Accordingly, a lower scan time may be achieved and/or moretime per projection may be employed to improve SNR.

FIG. 9 provides a schematic view of an example detector system 900having first detector 910 and second detector 920 mounted to a gantrythat may be used to image an object 902 having an ROI 904. (It may benoted only two detectors are shown for ease of illustration; however,additional detectors may also be mounted to the gantry.) As seen in FIG.9, the first detector 910 may have a default position 912, and beshifted by an angle 915 to a shifted position 914. The shifted position914 provides a different field of view 918 than the field of view 916corresponding to the default position 912. Depending on the size of theROI, shape of the ROI, position of the ROI relative to the detectors, orthe like, shifting the gantry position may provide a reduced number ofviews for all detectors combined. For example, the effect of shiftingmay be determined by determining the required views for the group ofdetectors at a number of different shift positions, and selecting theshift amount that provides the fewest required views. The shiftedposition 914 may be used for a first rotational step, with subsequentrotational steps taken at positions a predetermined angular stepdistance from the first rotational step.

With continued reference to FIG. 1, at 116, a larger percentage of timeis spent imaging the ROI to detectors in the identified set relative todetectors not in the identified set. In various embodiments, thedetectors selected to the identified set (e.g., at step 108), may bereferred to as a primary subset, and have an increased focus timepercentage to help avoid reducing time per projection when a wide ROI isdesired. However, for the detectors not in the primary subset, morenarrow ROI coverage may be allowed, leading to less views for thesedetectors in the focus ROI and decreased focus percentage (or time spentin focus region or ROI), which allows, for example, spending more timein other regions to help compensate for areas where the detectors in theprimary subset spend little or no time (e.g., background, or objectboundaries).

The use of different focus percentages (e.g., percentage of time spenton an ROI) may be tailored for particular portions of anatomy. Forexample, in some scans, the ROI is the striatum. Detectors that arerelatively far from the striatum tend to have lower resolution and lowercounts than those close to the striatum, with the detectors closer tothe striatum having a relatively higher contribution to image quality.Accordingly, those detectors closer to the striatum may be selected asthe primary subset, and have a relatively high focus percentage, andused to acquire mainly (or entirely) information from the focus regionor ROI, with minimal (or zero) background acquisition. In contrast,those detectors farther from the striatum may be omitted form theprimary subset, and used to acquire information from one or more out offocus regions (e.g., portions of the object outside the ROI) to improvebackground image quality.

It may be noted that the focus criteria or profile may be definedindependently for all detectors using a fixed focus or minimal time perprojection, allowing flexibility for scanning different object regions.

Returning to FIG. 1, at 118, the gantry and detector units arecontrolled to acquire imaging information. The determined sweepingconfiguration and rotational movement configuration define movements ofthe gantry and detector units, and time spent at each position betweenwhich they move, during the acquisition. Accordingly, the gantry and setof detector units are controlled utilizing the determined rotationalmovement configuration and sweeping configuration during acquisition ofimaging information. At 120, an image is reconstructed using the imaginginformation acquired at 118.

FIG. 10 provides a schematic view of a nuclear medicine (NM) multi-headimaging system 1000 in accordance with various embodiments. Generally,the imaging system 1000 is configured to acquire imaging information(e.g., photon counts) from an object to be imaged (e.g., a humanpatient) that has been administered a radiopharmaceutical. The depictedimaging system 1000 includes a gantry 1010 and a processing unit 1020.

The gantry 1010 defines a bore 1012. The bore 1012 is configured toaccept an object to be imaged (e.g., a human patient or portionthereof). As seen in FIG. 10, plural detector units 1015 are mounted tothe gantry 1010. In the illustrated embodiment, each detector unit 1015includes an arm 1014 and a head 1016. The arm 1014 is configured toarticulate the head 1016 radially toward and/or away from a center ofthe bore 1012 (and/or in other directions), and the head 1016 includesat least one detector, with the head 1016 disposed at a radially inwardend of the arm 1014 and configured to pivot to provide a range ofpositions from which imaging information is acquired. As discussedabove, in various embodiments, the gantry 1010 moves in rotationalsteps, with the detector units 1015 moving with the gantry 1010 over therotational steps.

The detector of the head 1016, for example, may be a semiconductordetector. For example, a semiconductor detector various embodiments maybe constructed using different materials, such as semiconductormaterials, including Cadmium Zinc Telluride (CdZnTe), often referred toas CZT, Cadmium Telluride (CdTe), and Silicon (Si), among others. Thedetector may be configured for use with, for example, nuclear medicine(NM) imaging systems, positron emission tomography (PET) imagingsystems, and/or single photon emission computed tomography (SPECT)imaging systems.

In various embodiments, the detector may include an array of pixelatedanodes, and may generate different signals depending on the location ofwhere a photon is absorbed in the volume of the detector under a surfaceif the detector. The absorption of photons from certain voxelscorresponding to particular pixelated anodes results in chargesgenerated that may be counted. The counts may be correlated toparticular locations and used to reconstruct an image.

In various embodiments, each detector unit 1015 may define acorresponding view that is oriented toward the center of the bore 1012.Each detector unit 1015 in the illustrated embodiment is configured toacquire imaging information over a sweep range corresponding to the viewof the given detector unit. FIG. 11 illustrates a detector arrangement2000 in accordance with various embodiments. The detector units of FIG.10, for example, may be arranged in accordance with aspects of thedetector arrangement 2000. In some embodiments, the system 1000 furtherincludes a CT (computed tomography) detection unit 1040. The CTdetection unit 1040 may be centered about the bore 1012. Images acquiredusing both NM and CT by the system are accordingly naturally registeredby the fact that the NM and CT detection units are positioned relativeto each other in a known relationship. A patient may be imaged usingboth CT and NM modalities at the same imaging session, while remainingon the same bed, which may transport the patient along the common NM-CTbore 1012.

As seen in FIG. 11, the detector arrangement 2000 includes detectorunits 2010(a), 2010(b), 2010(c), 2010(d), 2010(e), 2010(f), 2010(g),2010(h), 2010(i), 2010(j), 2010(k), 210(1) disposed about and orientedtoward (e.g., a detection or acquisition surface of the detector units,and/or the FOV (Field Of View), are oriented toward) an object 2002 tobe imaged in the center of a bore. Each detector unit of the illustratedembodiment defines a corresponding view that may be oriented toward thecenter of the bore of the detector arrangement 2000 (it may be notedthat because each detector unit may be configured to sweep or rotateabout an axis, the FOV need not be oriented precisely toward the centerof the bore, or centered about the center of the bore, at all times).The view for each detector unit 2010, for example, may be aligned alonga central axis of a corresponding arm (e.g., arm 1014) of the detectorunit 2010. In the illustrated embodiment, the detector unit 2010(a)defines a corresponding view 2020(a), the detector unit 2010(b) definesa corresponding view 2020(b), the detector unit 2010(c) defines acorresponding view 2020(c), and so on. The detector units 2010 areconfigured to sweep or pivot (thus sweeping the corresponding FOV's)over a sweep range (or portion thereof) bounded on either side of a linedefined by the corresponding view during acquisition of imaginginformation. Thus, each detector unit 2010 may collect information overa range larger than a field of view defined by a stationary detectorunit. It may be noted that, generally, the sweeping range over which adetector may potentially pivot may be larger than the corresponding viewduring acquisition. In some cameras, the sweeping range that a detectormay pivot may be unlimited (e.g., the detector may pivot a full 360degrees), while in some embodiments the sweeping range of a detector maybe constrained, for example over 180 degrees (from a −90 degree positionto a +90 degree position relative to a position oriented toward thecenter of the bore). It may be noted that the detector units 2010 ofFIG. 11 are mounted to a gantry 2030. The gantry 2030 may be rotatableto different positions (e.g., rotational steps), with the detector units2010 rotating with the gantry 2030. For example, with the gantry 2030 ina first position (e.g., as seen in FIG. 11), the individual detectorunits 2010 may be swept to acquire a first set or amount of imaginginformation. Then, the gantry 2030 may be moved to a second position(e.g., rotated to a new position, with the detector units 2010 moving orrotating with the gantry 2030). With the gantry 2030 in the secondposition, the individual detector units 2010 may be swept again toacquire a second set or amount of imaging information.

With continued reference to FIG. 10, the depicted processing unit 1020is configured to acquire imaging information via the detector units1015. In various embodiments as discussed herein, the imaginginformation acquired by the processing unit 1020 in various embodimentsincludes focused imaging information (e.g., from the ROI) and backgroundimaging information (from outside the ROI).

In various embodiments the processing unit 1020 includes processingcircuitry configured to perform one or more tasks, functions, or stepsdiscussed herein (e.g., to determine sweeping and/or rotational movementconfigurations, to identify a subset of detectors, to control detectorsand/or a gantry to acquire imaging information, and/or to reconstruct animage using acquired imaging information). It may be noted that“processing unit” as used herein is not intended to necessarily belimited to a single processor or computer. For example, the processingunit 1020 may include multiple processors, FPGA's, ASIC's and/orcomputers, which may be integrated in a common housing or unit, or whichmay distributed among various units or housings (e.g., one or moreaspects of the processing unit 1020 may be disposed onboard one or moredetector units, and one or more aspects of the processing unit 1020 maybe disposed in a separate physical unit or housing). The processing unit1020, for example, may control the detector heads to acquire desiredamounts of focused and background information, and/or reconstruct animage as discussed herein. It may be noted that operations performed bythe processing unit 1020 (e.g., operations corresponding to processflows or methods discussed herein, or aspects thereof) may besufficiently complex that the operations may not be performed by a humanbeing within a reasonable time period. For example, providing controlsignals to detector units, reconstructing images, or the like may relyon or utilize computations that may not be completed by a person withina reasonable time period.

In the illustrated embodiment, the processing unit 1020 includes areconstruction module 1022, a control module 1024, and a memory 1030. Itmay be noted that other types, numbers, or combinations of modules maybe employed in alternate embodiments, and/or various aspects of modulesdescribed herein may be utilized in connection with different modulesadditionally or alternatively. Generally, the various aspects of theprocessing unit 1020 act individually or cooperatively with otheraspects to perform one or more aspects of the methods, steps, orprocesses discussed herein.

In the illustrated embodiment, the depicted reconstruction module 1022is configured to reconstruct an image. The depicted control module 1024is configured to control the detector heads 1016 to sweep overcorresponding acquisition ranges to acquiring focused imaginginformation and background imaging information as discussed herein. Itmay be noted that, in various embodiments, aspects of the control module1024 may be distributed among detector units 1015. For example, eachdetector unit may have a dedicated control module disposed in the head1016 of the detector unit 1015.

The memory 1030 may include one or more computer readable storage media.The memory 1030, for example, may store information describingpreviously determined control information (e.g., sweeping configuration,rotational step configuration), parameters to be used for reconstruction(e.g., regularization weight parameter, number of iterations) or thelike. Further, the process flows and/or flowcharts discussed herein (oraspects thereof) may represent one or more sets of instructions that arestored in the memory 1030 for direction of operations of the imagingsystem 1000.

It may be noted that while the processing unit 1020 is depictedschematically in FIG. 10 as separate from the detector units 1015, invarious embodiments, one or more aspects of the processing unit 1020 maybe shared with the detector units 1015, associated with the detectorunits 1015, and/or disposed onboard the detector units 1015. Forexample, in some embodiments, at least a portion of the processing unit1020 is integrated with at least one of the detector units 1015.

It should be noted that the particular arrangement of components (e.g.,the number, types, placement, or the like) of the illustratedembodiments may be modified in various alternate embodiments, and/or oneor more aspects of illustrated embodiments may be combined with one ormore aspects of other illustrated embodiments. For example, in variousembodiments, different numbers of a given module or unit may beemployed, a different type or types of a given module or unit may beemployed, a number of modules or units (or aspects thereof) may becombined, a given module or unit may be divided into plural modules (orsub-modules) or units (or sub-units), one or more aspects of one or moremodules may be shared between modules, a given module or unit may beadded, or a given module or unit may be omitted.

As used herein, a structure, limitation, or element that is “configuredto” perform a task or operation is particularly structurally formed,constructed, or adapted in a manner corresponding to the task oroperation. For purposes of clarity and the avoidance of doubt, an objectthat is merely capable of being modified to perform the task oroperation is not “configured to” perform the task or operation as usedherein. Instead, the use of “configured to” as used herein denotesstructural adaptations or characteristics, and denotes structuralrequirements of any structure, limitation, or element that is describedas being “configured to” perform the task or operation. For example, aprocessing unit, processor, or computer that is “configured to” performa task or operation may be understood as being particularly structuredto perform the task or operation (e.g., having one or more programs orinstructions stored thereon or used in conjunction therewith tailored orintended to perform the task or operation, and/or having an arrangementof processing circuitry tailored or intended to perform the task oroperation). For the purposes of clarity and the avoidance of doubt, ageneral purpose computer (which may become “configured to” perform thetask or operation if appropriately programmed) is not “configured to”perform a task or operation unless or until specifically programmed orstructurally modified to perform the task or operation.

As used herein, the term “computer,” “processor,” or “module” mayinclude any processor-based or microprocessor-based system includingsystems using microcontrollers, reduced instruction set computers(RISC), application specific integrated circuits (ASICs), logiccircuits, and any other circuit or processor capable of executing thefunctions described herein. The above examples are exemplary only, andare thus not intended to limit in any way the definition and/or meaningof the term “computer,” “processor,” or “module.”

The computer or processor executes a set of instructions that are storedin one or more storage elements, in order to process input data. Thestorage elements may also store data or other information as desired orneeded. The storage element may be in the form of an information sourceor a physical memory element within a processing machine.

The set of instructions may include various commands that instruct thecomputer or processor as a processing machine to perform specificoperations such as the methods and processes of the various embodiments.The set of instructions may be in the form of a software program. Thesoftware may be in various forms such as system software or applicationsoftware. Further, the software may be in the form of a collection ofseparate programs or modules, a program module within a larger programor a portion of a program module. The software also may include modularprogramming in the form of object-oriented programming. The processingof input data by the processing machine may be in response to operatorcommands, or in response to results of previous processing, or inresponse to a request made by another processing machine.

As used herein, the terms “software” and “firmware” may include anycomputer program stored in memory for execution by a computer, includingRAM memory, ROM memory, EPROM memory, EEPROM memory, and non-volatileRAM (NVRAM) memory. The above memory types are exemplary only, and arethus not limiting as to the types of memory usable for storage of acomputer program.

It is to be understood that the above description is intended to beillustrative, and not restrictive. For example, the above-describedembodiments (and/or aspects thereof) may be used in combination witheach other. In addition, many modifications may be made to adapt aparticular situation or material to the teachings of the variousembodiments without departing from their scope. While the dimensions andtypes of materials described herein are intended to define theparameters of the various embodiments, the embodiments are by no meanslimiting and are exemplary embodiments. Many other embodiments will beapparent to those of skill in the art upon reviewing the abovedescription. The scope of the various embodiments should, therefore, bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

In the appended claims, the terms “including” and “in which” are used asthe plain-English equivalents of the respective terms “comprising” and“wherein.” Moreover, in the following claims, the terms “first,”“second,” and “third,” etc. are used merely as labels, and are notintended to impose numerical requirements on their objects. Further, thelimitations of the following claims are not written inmeans-plus-function format and are not intended to be interpreted basedon 35 U.S.C. § 112(f), unless and until such claim limitations expresslyuse the phrase “means for” followed by a statement of function void offurther structure.

This written description uses examples to disclose the variousembodiments, including the best mode, and also to enable any personskilled in the art to practice the various embodiments, including makingand using any devices or systems and performing any incorporatedmethods. The patentable scope of the various embodiments is defined bythe claims, and may include other examples that occur to those skilledin the art. Such other examples are intended to be within the scope ofthe claims if the examples have structural elements that do not differfrom the literal language of the claims, or if the examples includeequivalent structural elements with insubstantial differences from theliteral language of the claims.

What is claimed is:
 1. A nuclear medicine (NM) multi-head imaging systemcomprising: a gantry defining a bore configured to accept an object tobe imaged, the gantry configured to rotate about the bore; pluraldetector units mounted to the gantry and configured to rotate as a groupwith the gantry around the bore in rotational steps, each detector unitconfigured to sweep about a corresponding axis and acquire imaginginformation while sweeping about the corresponding axis; and at leastone processor operably coupled to at least one of the detector units,the at least one processor configured to: determine a region of interest(ROI) of the object to be imaged; identify a set of detector units fromthe plural detector units mounted to the gantry; for the identified setof detector units, determine a sweeping configuration that results in apredetermined percentage of projection pixels receiving information fromthe ROI; determine a rotational movement configuration for the gantryusing the determined sweeping configuration; and control the gantry andthe set of detector units to utilize the determined rotational movementand sweeping configurations during acquisition of imaging information.2. The system of claim 1, wherein the identified set of detector unitsis a subset of the plural detector units determined based on at leastone of a proximity to the ROI or corresponding attenuation to thedetector units.
 3. The system of claim 1, wherein the predeterminedpercentage varies among at least some of the detector units.
 4. Thesystem of claim 1, wherein the at least one processor is configured todetermine the rotational movement configuration to provide a minimalnumber of views from the identified set of detectors for each rotationstep.
 5. The system of claim 1, wherein the at least one processor isconfigured to determine the rotational movement configuration to providea minimal number of views from the identified set of detectors summedover all rotation steps.
 6. The system of claim 1, wherein the at leastone processor is configured to assign a larger percentage of time spentimaging the ROI to detectors in the identified set than to detectors notin the identified set.
 7. The system of claim 1, wherein the at leastone processor is configured to determine a total number of rotationalsteps to be taken by the gantry before determining the sweepingconfigurations.
 8. A method for acquiring imaging information with anuclear medicine (NM) multi-head imaging system comprising a gantry andplural detector units, the gantry defining a bore configured to acceptan object to be imaged, the gantry configured to rotate about the bore,the plural detector units mounted to the gantry and configured to rotateas a group with the gantry around the bore, each detector unitconfigured to sweep about a corresponding axis and acquire imaginginformation while sweeping about the corresponding axis, the methodcomprising: determining a region of interest (ROI) of the object to beimaged; identifying a set of detector units from the plural detectorunits mounted to the gantry; for the identified set of detector units,determining a sweeping configuration that results in a predeterminedpercentage of projection pixels receiving information from the ROI;determining rotational movement configuration for the gantry using thedetermined sweeping configuration; and controlling the gantry and theset of detector units to utilize the determined rotational movement andsweeping configurations during acquisition of imaging information. 9.The method of claim 8, wherein identifying the set of detector unitscomprises identifying a subset of the plural detector units based on atleast one of a proximity to the ROI or corresponding attenuation to thedetector units.
 10. The method of claim 8, wherein the predeterminedpercentage varies among at least some of the detector units.
 11. Themethod of claim 8, further comprising determining the rotationalmovement configuration to provide a minimal number of views from theidentified set of detectors for each rotation step.
 12. The method ofclaim 8, further comprising determining the rotational movementconfiguration to provide a minimal number of views from the identifiedset of detectors summed over all rotation steps.
 13. The method of claim8, further comprising assigning a larger percentage of time spentimaging the ROI to detectors in the identified set relative to detectorsnot in the identified set.
 14. The method of claim 8, further comprisingdetermining a total number of steps to be taken by the gantry beforedetermining the sweeping configurations.
 15. A nuclear medicine (NM)multi-head imaging system comprising: a gantry defining a boreconfigured to accept an object to be imaged, the gantry configured torotate about the bore; plural detector units mounted to the gantry andconfigured to rotate as a group with the gantry around the bore inrotational steps, each detector unit configured to sweep about acorresponding axis and acquire imaging information while sweeping aboutthe corresponding axis; and at least one processor operably coupled toat least one of the detector units, the at least one processorconfigured to: determine a region of interest (ROI) of the object to beimaged; for at least one of a number of different total rotational stepcombinations, determine gaps resulting between detector views for eachrotational step combination; determine a number of rotational steps tobe used based on the gaps; and control the gantry and the set ofdetector units using the determined number of rotational steps duringacquisition of imaging information.
 16. The system of claim 15, whereindetermining the gaps resulting between the detector views comprises:determining detector positions and angles for all views of therotational step combination; arrange the detector views in binsaccording to view angle; for each bin, project each detector view alongthe view angle to find a start and end position for each correspondingdetector; for each bin, determine the maximum gap between the projectedviews; and determine a largest gap of the maximum gaps determined foreach bin.
 17. The system of claim 15, wherein the number of rotationalsteps is determined to satisfy a predetermined maximum threshold gapsize.
 18. The system of claim 15, wherein the gap is determinediteratively, wherein the at least one processor is configured todetermine resulting gaps for an initial number of rotational steps,compare the resulting gaps to a threshold, and, if the resulting gaps donot satisfy the threshold, increase the number of rotational steps. 19.The system of claim 15, wherein the at least one processor is configuredto determine a size of the ROI, and determine the number of rotationalsteps based on the size of the ROI.
 20. The system of claim 19, whereinthe at least one processor is configured to use the determined number ofrotational steps as an initial number of rotational steps for aniterative determination of rotational steps.